The Plant Body

1. The Plant Body

2. Early Stem Growth – the Plumule

3. Plant Growth – Apical Dominance

4. Stem Function • Conduction involves moving substances manufactured in the leaves through the phloem to other parts of the plant including developing leaves, stems, roots, developing flowers, seeds and fruits • The xylem carries water from the roots to the leaves, where water is transpired • Support involves holding the plant off the ground • Stems may function to a certain extent in storage as well, storing material in parenchyma cells

6. Primary Growth of the Stem • The apical meristem adds cells to the plant body and forms leaf primordia and bud primordia that develop into lateral branches • The apical meristem of a stem lacks a protective cover like the root cap of roots • Protoderm always originates from the outermost meristem cell layer • Procambium and part of the ground meristem (which will form the cortex and sometimes part of the pith) form from the peripheral meristem • The rest of the ground meristem (which forms some or all of the pith) is formed by the pith meristem

8. Stem Growth

9. Position of shoot meristems – shown by black dot

11. Increase in primary thickness • Growth in thickness of the primary body of the stem involves longitudinal division and cell enlargement in both cortex and pith - in plants with secondary growth, primary thickening of the stem is moderate • Monocots usually lack secondary growth, but may have massive primary thickening and growth (palms)

12. Monocot primary growth

13. Primary and Secondary Stem Growth

14. Primary Stem Structure • In some conifers and dicots, the narrow, elongated procambial cells (and consequently the primary vascular tissues that develop from them) appear as a more or less continuous hollow cylinder within the ground tissue - the outer region of the ground tissue is called the cortex and the inner region is the pith • A good example of this structure is basswood - Tilia – it has secondary growth

15. Basswood or Linden (Tilia)

16. Primary Stem Structure • In other conifers and dicots, the primary vascular tissues develop as a cylinder of discrete strands separated from one another by ground tissue • The ground tissue separating the procambial strands (and later mature vascular bundles) is continuous with cortex and pith and is called the interfascicular parenchyma (between the bundles) • The interfascicular regions are often called pith rays

17. Sunflower Stem Structure

18. Primary Stem Structure • In most monocots and some herbaceous dicots, the arrangement of procambial strands and vascular bundles is more complex - vascular tissues do not appear as a single ring, but instead develop as more than one ring or are scattered throughout the ground tissue - here ground tissue cannot be distinguished as pith and cortex – seen in corn

19. Corn (Zea mays) stem structure

20. Relationship of vascular tissue in leaves and stem • The pattern formed by the vascular bundles in the stem reflects the close structural and developmental relationship between the stem and its leaves • at each node, one or more vascular bundles diverge from the cylinder of strands in the stem, cross the cortex and enter the leaf or leaves attached at that node • The extensions from the vascular system in the stem toward the leaves are called the leaf traces

21. Relationship of vascular tissue in stems and vascular bundles

23. Leaf Traces and Stem Bundles • If stem bundles are followed either upward or downward in the stem, they will be found to be associated with several leaf traces - a stem bundle and its associated leaf traces are called a sympodium • In stems of some species, some or all or the sympodia are interconnected • In other species, all the sympodia are independent units of the vascular system

24. Vascular bundles are frequently arranged in spiral fashion

25. Leaf Structure

29. Leaf Internal Structure • variations in internal structure of leaves are largely due to growth habit of the plant • mesophytes are plants that require abundant soil moisture and a fairly humid environment - the most common plants - typically have fairly well developed epidermis, especially on upper surface of leaf, stomata on both sides of leaf • hydrophyte - plants that depend on a very abundant supply of water or which grow wholly or partially submerged in water - have thin epidermis, stomata only on upper surface • xerophyte - plants adapted to arid habitats - very thick epidermis, stomata open to stomatal crypts with protective hairs

30. Mesophyte Leaf

31. Hydrophyte Leaf

32. Xerophyte Leaf

35. Dicot stomata

36. Leaf Venation

37. Leaf Venation

38. Bulliform cells and leaf curling

39. Sun vs. Shade Leaves in Oaks